Organ and cell culture studies using buccal mucosa from zinc-deficient rats, will be conducted. Zinc concentration and distribution will be determined by means of atomic absorption spectrophotometry and scanning electron microscopy X-ray microanalysis. Capillaries will be visualized by means of histochemical demonstration of their alkaline phosphatase activity, permitting tracing and measurement. The size of the capillary bed in the lamina propria of regions of oral epithelium differing in width will be determined in two groups of rats ages 18 and 24 months.